The field of the invention is that of accelerometers, and the invention relates more particularly to silicon accelerometers for use in automotive safety air bag applications.
Conventional silicon accelerometers comprise a silicon mass which is movable in a silicon body relative to an integral silicon support to provide strain in the silicon body in response to acceleration of the body. Piezoresistive sensor means are formed in the silicon body material to be responsive to the strain to provide an electrical signal corresponding to the acceleration. The silicon body is mounted on an object whose acceleration is to be monitored, and the piezoresistive sensors are connected in a signal conditioning circuit to provide a control signal corresponding to acceleration of the object. It has been proposed that such accelerometers are particularly adapted for sensing automotive vehicle acceleration for regulating operation of safety air bag systems.
Frequently, when such accelerometers are proposed for use in automotive environments, it is found that the silicon body materials, the materials used in mounting the accelerometer in a vehicle and the materials used in electrically connecting piezoresistive sensors on the silicon body into a vehicle circuit display substantially different coefficients of thermal expansion. Some portions of the accelerometer also have to be fixed to a vehicle mount with secure clamping forces. Accordingly when such materials are subjected to widely varying temperature conditions likely to be encountered during automotive vehicle use, which temperatures typically vary over a range from -40.degree. C. to 85.degree. C., the silicon body of the accelerometer tends to be subjected to strain due to the noted differences in thermal expansion properties so that the accuracy of output signal provided by the accelerometer is deleteriously affected by the strain.